small question about tape-based dumps

Karl Vogel vogelke+unix at
Sat Oct 17 22:30:42 UTC 2009

>> On Fri, 16 Oct 2009 17:37:32 -0400, 
>> Jerry McAllister <jerrymc at> said:

J> You can easily put more than one dump on a tape if there is room enough
J> for them.  I actually rewind and skip between each dump of multiples
J> made to the same tape.  I also use the no-rewind device for the tape.

   Whenever possible, I set aside a 4-8 Gb partition for a staging area.
   This has helped me avoid several nasty tape problems:

   a. Dump to a file on the staging area, compressing it if possible.
   b. Get an MD5/SHA1/whatever signature for the dump.
   c. Write it to tape.

   When all the dumps are finished, rewind the tape.  Read each tape file,
   get the signature, and compare it to what you got before; this way,
   you know your backup is good.  Tapes stretch and wrinkle, tape heads
   get out of alignment, tapes can "bleed" over time, etc.  There are few
   things worse than trying to restore someone's file and finding out you
   have a screwed backup.

   Another advantage of a staging area is better tape use; if you're
   copying a single file to tape (most of which is still in cache from
   the signature check), the tape drive won't spend as much time polishing
   the heads waiting for something to write.

Karl Vogel                      I don't speak for the USAF or my company

The RAID was dirty *and* degraded (insert "your mom" joke here).
                        --Mike Markley on Slashdot discussing Linux drives

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